Cigarette smoking is the largest preventable risk factor for morbidity and mortality in developed countries. Despite an increasing number of pharmacological and psychosocial treatments for smoking, over 20% of Americans continue to smoke. The limitations of current interventions point to the need for innovative and powerful behavioral therapies for smoking. Abstinence reinforcement therapy is one such treatment. To apply abstinence reinforcement therapy to smoking, we developed a home-based monitoring system to obtain objective measures of smoking status. The system uses Internet technology to obtain video of smokers providing carbon monoxide samples, which is a simple yet innovative way to verify smoking status on a frequent and sustained basis. Voucher reinforcement produced substantial reductions in smoking and sustained abstinence in heavy smokers. In light of these encouraging data, we are proposing to replicate and extend our current results in a three-year study. The home-based system will allow us to deliver a high dose behavioral treatment during the initial weeks of a quit attempt. This is a critical period: abstinence during the first few weeks of a cessation effort is strongly associated with long-term success, and most smokers relapse within the first week of a quit attempt. Furthermore, several recent studies suggest that experimentally inducing abstinence with voucher reinforcement produces increased motivation to quit and lasting effects, even for smokers with no plans to quit. Voucher reinforcement also lowers ratings on a number of key measures associated with relapse risk. It remains to be seen whether these experimentally induced changes in motivation and relapse risk do, in fact, translate into lower relapse rates. Heavy smokers will be randomly assigned to a voucher reinforcement or a non-contingent voucher reinforcement control condition. We will measure motivation to quit, relapse risk, rates of initial abstinence during treatment, and smoking status at a six-month follow up. The proposed study will be the first to provide valuable data about the relation between voucher-induced changes in key measures of relapse risk and relapse rates in heavy smokers, and the efficacy of applying an intensive behavioral treatment during a critical period of a quit attempt. The home-based voucher program may prove to be rigorous and convenient method to initiate and maintain high levels of abstinence, particularly in high-risk groups. As such, it may hold significant promise as a way to reduce the high rates of morbidity and mortality associated with smoking.